Cellular and other data communication service providers operate in accordance with communication standards. Often, communication standards are adopted only after difficult and lengthy negotiations and design efforts by competing interests who are technically knowledgeable about a variety of potential, realizable communication schemes. After a hard-fought standard is eventually adopted, service providers and their customers then procure, install, and operate a vast amount of expensive equipment conforming to the standard.
But as technical capabilities evolve, standards become outdated. A need exists to gracefully migrate from an older standard which is supported by an entire infrastructure of service-provider and user equipment to a newer standard. A graceful migration should support newer equipment that may provide enhanced communication services in accordance with a newer standard as such equipment becomes available while also supporting a population of legacy equipment that complies with an older standard.
One family of communication standards that has been successful in recent years was ratified by the International Telecommunication Union (ITU) and given the designation “IS-856”. This standard is concerned with wideband, wireless data communications, and has been associated with a variety of common names including: CDMA2000, Evolution-Data Only, Evolution-Data Optimized, EV-DO, EVDO, 1xEV-DO, and the like. This family of standards has successfully evolved from a “Rev-0” revision, through a “Rev-A”, a “Rev-B”, and a “Rev-C” revision. Future revisions may revise the family of standards even further.
The EV-DO standards define spread spectrum communication schemes. The different revisions of the EV-DO standards provide for higher data rates primarily by accommodating parallel operation of multiple EV-DO channels. But the basic definition of an EV-DO channel remains essentially as originally envisioned so that legacy equipment is supported for graceful transitions to newer standards. Some of the basic characteristics of an EV-DO channel are a chip rate of 1.288 mcps and an excess-bandwidth factor “a” of about 1.22, resulting in a bandwidth requirement of around 1.5 MHz for a single EV-DO channel. The later revisions define how to operate multiple ones of these EV-DO channels in parallel so that increased data rates result. The later revisions contemplate operating EV-DO channels in parallel over up to a 20 MHz bandwidth, and the 20 MHz need not be provided in a contiguous band.
The goal of any communication system, including systems operated in accordance with the EV-DO standards and those operated in accordance with competing standards, is to communicate the most data possible, after identifying and correcting errors, using the least amount of bandwidth while adhering to regulatory and power consumption constraints. A communication system should use its allocated bandwidth as efficiently as possible to accomplish this goal. But conventional communication systems operated in accordance with the later revisions of the EV-DO standards tend use their bandwidths inefficiently.
Historical precedence and practicality has led to regulatory allocation of bandwidth in integral multiples of 5 MHz in the region of the electromagnetic spectrum where EV-DO and competing systems operate. While 1.25 MHz and 2.5 MHz contiguous bands might possibly be allocated, contiguous bands of 5 MHz are commonly allocated, with the occasional contiguous band of up to 20 MHz being allocated from time-to-time and location-to-location.
FIG. 1 shows a representative conventional allocation of a 5 MHz contiguous frequency band, shown as extending from −2.5 MHz to +2.5 MHz, for use by three EV-DO channels. The 5 MHz contiguous band is not efficiently used by three EV-DO channels, which each require its own approximately 1.5 MHz bandwidth. Some portions of the 5 MHz channel are not carrying any appreciable amount of energy that may be otherwise used to communicate data. In other words, the conventional allocation can communicate no more data through a 5 MHz contiguous frequency band than it could through a 4.5 MHz contiguous band or through three non-contiguous 1.5 MHz bands. A need exists for a better match between EV-DO channel bandwidth requirements and the actual amounts of contiguous bandwidths that tend to be allocated by regulatory agencies.
Communication schemes that compete with the EV-DO family of communication standards are better able to efficiently utilize differing amounts of allocated bandwidths. Such schemes are often based on orthogonal frequency division multiplex (OFDM) techniques. OFDM better utilizes diverse bandwidths by subdividing a given allocated bandwidth into a multiplicity of sub-channels, wherein the sub-channels avoid the insertion of inefficient frequency guard bands by adhering to an “orthogonality” constraint. But OFDM techniques utterly fail to support an existing population of legacy equipment that complies with EV-DO standards. Likewise, hybrid OFDM/CDMA communication schemes have been proposed that may better utilize diverse bandwidths than conventional EV-DO communication systems can. But, such communication schemes also utterly fail to support an existing population of legacy equipment that complies with EV-DO standards.
Accordingly, a need exists for communication system components and for a method of operating communication system components that support the efficient use of multiple EV-DO channels in the bandwidths that are typically allocated by regulatory agencies.